The present invention is illustrated and described in terms of a burnisher, but persons skilled in the art will readily appreciate that the principle of the invention is generally applicable to other machines wherein it is desired to control the operating pressure of a floor-engaging work unit such as a brush or pad. The term "operating pressure" refers to the downward force induced by the work unit on the floor being treated.
U.S. Pat. No. 4,674,142 discloses a floor cleaning machine with an electrical motor for controlling the position of a brush head relative to the floor. In one embodiment, a pressure sensing device is mounted on a lever arm for carrying the brush head. A control motor positions a gear block which is connected to the lever by a spring for setting the applicator pressure on the brush head. In a second embodiment, it is suggested that the mounting lever carrying the brush head be set by the control motor by means of pulse width modulation such that "the stall-voltage of the motor means [i.e., the control motor] is maintained at an operator-set value".